linux-kernel - Re: [PATCH v5 2/2] sched/fair: update scale invariance of PELT

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Message-ID: <145bfbd2-f07f-6312-ca2f-029a5301fb15@arm.com>
Date:   Thu, 1 Nov 2018 10:38:22 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Morten Rasmussen <Morten.Rasmussen@....com>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Paul Turner <pjt@...gle.com>, Ben Segall <bsegall@...gle.com>,
        Thara Gopinath <thara.gopinath@...aro.org>,
        pkondeti@...eaurora.org
Subject: Re: [PATCH v5 2/2] sched/fair: update scale invariance of PELT

On 10/31/18 10:18 AM, Vincent Guittot wrote:
> Hi Dietmar,
> 
> On Wed, 31 Oct 2018 at 08:20, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
>>
>> On 10/26/18 6:11 PM, Vincent Guittot wrote:
>>
>> [...]
>>
>>>    static int select_idle_sibling(struct task_struct *p, int prev_cpu, int cpu);
>>>    static unsigned long task_h_load(struct task_struct *p);
>>> @@ -764,7 +763,7 @@ void post_init_entity_util_avg(struct sched_entity *se)
>>>                         * such that the next switched_to_fair() has the
>>>                         * expected state.
>>>                         */
>>> -                     se->avg.last_update_time = cfs_rq_clock_task(cfs_rq);
>>> +                     se->avg.last_update_time = cfs_rq_clock_pelt(cfs_rq);
>>>                        return;
>>>                }
>>>        }
>>
>> There is this 1/cpu scaling of se->avg.util_sum (running_sum) in
>> update_tg_cfs_runnable() so it can be used to calculate
>> se->avg.runnable_load_sum (runnable_sum). I guess with your approach
>> this should be removed.
> 
> Yes good catch

Another thing, since you do not need the cpu parameter in 
accumulate_sum() anymore, you could also get rid of it in 
___update_load_sum() and further in __update_load_avg_blocked_se(),
__update_load_avg_cfs_rq() and __update_load_avg_se().

Nitpick: The function header of update_cfs_rq_load_avg() mentions '@now: 
current time, as per cfs_rq_clock_task()' ... should mention 
cfs_rq_clock_pelt() instead.

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